The present invention relates to generators for use in the near millimeter wave region of the spectrum, and more particularly to generators, operating in that portion of the spectrum, capable of modulation and generating a variable frequency signal.
The need for generation capability of frequencies in the 100 GHz to 1,000 GHz range is established, in areas such as radar for military application.
Prior art generators in this frequency range utilize an etched grating on a metallic surface. The grating provides an interruption in an electromagnetic field generated by a moving electron beam, thus generating a particular frequency which is a function of the spacing of the ruled lines in the grating, the velocity of the electron beam, and the angle at which the output is observed.
However, the utilization of a fixed, etched grating upon a metallic surface does not permit for variation of the output frequency except by variation of the velocity of the electron beam or of the angle of observation of the output result, both processes involving complicated procedures. Specific references in disclosing related devices include Volume SU-20, IEEE Transactions on Sonics and Ultrasonics, No. 2, April, 1973, pages 173 et seq, disclosing an acoustic signal storage device. However, no disclosure is provided of frequency variation methods or apparatus, and a disclosed structure utilizes a normally incident beam to store an acoustic pattern on a piezoelectric crystal. In a letter published in the Proceedings of the IEEE, February, 1970, pages 253-4, an electron beam, normally incident to an elastic surface, is used to read out surface waves on the surface.
In Volume 12, No. 5 of Soviet Physics-Solid State, November, 1970, pages 1189 et seq, plasma waves are used in a semiconductor in conjunction with an electron beam to provide energy to an acoustic wave. The electron beam is used to create a movement of charge in the surface, and plasma waves are set up to enhance the effect. While the reference discloses the interaction of an electron beam with a surface wave, the interaction relates to plasma surface waves in a semiconductor, and not to acoustic waves in a piezoelectric crystal as presently disclosed.
In Volume 18 of Soviet Physics-Solid State, No. 11, November, 1976, pages 1982 et seq, an article appears relating to amplification and generation of surface electro-acoustic waves at an interface between piezoelectric and nonpiezoelectric semiconductors. The concept, however, calls for transfer of energy into the surface acoustic waves, rather than the presently contemplated energy transfer from the acoustic waves via an electron beam to electromagnetic radiation in the near millimeter frequency range.
In summary, no prior art disclosures are known to the applicants which suggest either the concept or an apparatus for utilizing an interaction between an electron beam and a surface acoustic wave on a piezoelectric crystal to generate electromagnetic waves in the near millimeter spectrum, or the further variability or modulation of the output frequency of such generated waves by variation of the acoustic wave frequency.